Indirectly heated cathode



March 2, 1948f R. F. TRIMBLE INDIRECTLY HEATED CATHQDE Filed Juhe 23, 1945 INVENTOR RUSSELL F. TRIMBLE ATTORNEY v Patented Mar. z, 1948 mus. aattimfimataaaaa,

by hiesne assia'iihiem; $0 he, United; States pr War Application June 23,-

. ill. I My invention relates in general to electron discharge devices and more particularly to methods of constructing indirectly-heated cathodes for such devices. In the construction of indirectly-heated cathodes, it is customary to employ a shell of con ducting material coated with an electron emitting substance, a filament carrying heater cur rent being placed within the shell. The 'methods of disposing this heater element within the cathode vary, but clearly it is important to construct the filament so that most eflicient heating is obtained.

Accordingly, it is one object of my invention to provide an emciently heated indirectly-heated cathode. I

Another object is to provide a method of constructing a filament for a hollow cylindrical cathode. Still another object is toutilize most efllciently the space available within acathode for heating purposes.

These and otherobjects of my invention will be apparent to thoseskilled in the art upon reference to the following specification, claims, and drawings in which; i

Fig. 1 is an elevational view of a coil employed in my invention;

Fig. 2 is an end view of a cathode into which the heater element of the invention has been insertedyand,

-8 is a longitudinal section of a cathode. and a heater, shown in elevation, within the cathode. a

Referring now to Fig. 1, a wire 5 of any suitable ductile material, for. example molybdenum, is wound in an elongated spring sh ape with a minimum suitable radius of curvature at the ends of the coils'and being straight in the long sections. Thespring rnay be wound with the 9 facilitate packing into the" coils close together to at o i 1L,

It is next nagram-teat iiisuiaang matween the turns when heater "voltage is-applied. A convenient way of, doing this is to spray the wire with a fluid suspension of an insulating ceramic such as aluminum oxide. The coil should be slightly stretched to insure .that 'the. entire surface is covered bythe's'pray. The next :Americ'a, as represent?! by 194's:stalking-L119 iclafims. detest-i155).

turns are close to one another and baked again at 1600 C. until the insulating material is very hard.

. When this process has been completed the coil 5 is then rolled into a spiral form and is inserted into a suitable cathode shell I which may be a cylindrical nickel sleeve coated with electron missive material 8 as shown in Fig. 2. The free ends of the coil are allowed to project from the cathode shell to permit connection to any desirable form of terminal means. By employing areasonable amount of care, this operation may be performed without damaging the ceramic insulating coating.

As shown in-F'ig. 3, it is preferable that the cathode! should'be slightly longer than the coil in orderthat an insulating material 9 may be packed into both ends of the cathode. The rea- 1 sons fordoing this aretwo-fold: the filament is heldsecurelyin place thus preventing slipping oig'vibrattioii of-.the.wire, and wasteful radiation of'heat from thejends of the cathode is greatly lessened. It has been foundthat aluminum oxide serves well as'fthis insulating material.

,Thus it can ,be seen that my invention allows eflflcient use 'of the voliime within the cathode shell since the heater wire occupies. by far the greatest portionof the available space.

' It is tebefempnasizea that what has been'described herein isa preferred embodiment of my invention and certain deviations may be made therefrom without exercise of inventive ingenuity. Hence, I claim all; such modifications and adaptations which may fall fairly within the b b v irectlyheated cathode for a thermionic tube, said cathode coinprising a hollow, mey id er, an electron-emissive face of said cylinder and ,saidc'yunder, said heater uncompressed, helical, b g lie 'into'a flat spiral.

I indirctly'heated cathode as defined in which-,ithe fiuter side-surface; of said the diameter of which "t e inner diameter of said cathode cylinder, whereby said outer sidesurfa'ce isin direct "contact with the inner surface or said cathode'cylinder.

"3.1m indirectly heated cathode as defined in claim 1 in fwh'ich the said spiral is compactly wound-and inakes a snug fit within the cathode cylinder.

spirit and scope of the hereinafter appended 3 4. An indirectly heated cathode as defined in claim 1 in which said ribbon-shaped coil comprises a plurality of turns of insulated wire bent on itself whereby the thickness of said ribbonshaped coil is substantially equal to twice the thickness of said insulated wire. f,

5. An indirectly heated cathode as definedjn claim 1 in which said spiral has a. pluarlity of convolutions, each successive convolution snugly fitting over the preceding convolution, and in which the axis of said spiral is perpendicular to two parallel planes defined by the lower and upper edges of said ribbon.

6. An indirectly heated claim 1 in which the height of said flat spiral is substantially equal to the height of said electron emissive layer, the height of the latter being less than the height of said cathode cylinder,

RUSSELL F. TRIMBLE.

cathode 'a's defined in 4 summons crrsn The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain Oct. 12, 1936 

